1. Field of the Invention
The present invention relates to screw and nut assemblies and more particularly, to a screw and nut assembly with screw rod support means.
2. Description of the Related Art
In a machine using a screw and nut set, the platform for carrying workpieces is affixed to the screw nut of the screw and nut set and movable with the screw nut forwardly and backwardly along the screw rod. To a screw and nut set that provides a relatively longer stroke, the screw rod has a relatively longer length. In this case, the screw rod has a greater tendency to deform during movement of the screw nut. During operation, the screw rod may be excessively deformed. As a result, the critical rotating speed of the screw rod will be constrained, and a high noise may be produced due to unsmooth movement between the screw rod and the screw nut. To avoid this problem, support means may be provided at the bottom side of the screw and nut set to support the screw rod, reducing the problems of screw rod deformation and constraint of critical rotating speed. FIG. 1 illustrates a prior art design with the arrangement of screw rod support means. According to this design, a connection rod 3 is connected between the screw nut 2 and each support 1, enabling each support 1 to be moved with the screw nut 2. Thus, the screw rod is well supported, minimizing deformation during operation. However, because the gap between each support 1 and the screw nut 2 is constant, the movable stroke of the screw nut 2 is relatively reduced due to the arrangement of the supports 1. FIG. 2 illustrates a pneumatic/hydraulic pressure-driven design according to the prior art. This design uses supports 4 to support the screw rod, and allows control of the positions of the supports 4 in supporting the screw rod to reduce the stroke in which the screw nut is stopped from movement. However, this pneumatic/hydraulic pressure-driven design is much expensive, limiting its applications.